The study will examine a methodological issue of major importance in descriptive studies of clinical reasoning and decision making. The principal methodological alternatives for such studies are direct observation of clinical performance, chart reviews, process tracing studies, and written cases. Written cases are efficient, permit more extensive sampling within constraints of time and money, and lend themselves to experimental control. However, extensive use of the method requires that the issues of external validity and clinical credibility be adequately addressed. The proposed research will assess the validity of brief written cases as a method for research in clinical reasoning and decision making. Test ordering behavior of physicians recorded in a computer based health information system will be compared with their responses to carefully designed and structured written cases. The research method draws on social judgment theory and standard measurement theory to address three related goals: 1) To assess the validity of written case vignettes for studying clinical decision making by analyzing the degree to which responses to written cases accurately reflect variation in actual clinical decisions. 2) To determine the effects of variation in design of case vignettes on data obtained, on the interpretation of data, and on external validity. 3) To assess how respondents' ratings of the credibility of structured vignettes are affected by design with correlated or uncorrelated cues. Test ordering will be examined for two clinical conditions. After preliminary analysis of the data base, urinary tract infection and hypertension were chosen on the basis of frequency, low or identifiable incidence of co-morbidity, known variation among physicians in number of kind of tests ordered, and absence of a standard algorithm for management. Statistical analyses will include multivariate analysis of variance, multiple regression and correlation techniques. Generalizability of written cases will be addressed by administering the materials to physicians in two family practice settings. The contribution of local context factors not represented in the cases will be assessed by analyzing differences in the correlations between responses to cases and actual test ordering in the two settings.